Thermoplastic components with reduced coefficient of thermal expansion

ABSTRACT

A composite structural component includes a longitudinally extending elongated base element and a plurality of longitudinally extending elongated reinforcing members each secured to the base element along a length of the reinforcing member at spaced apart locations on the base element. The base element is of a first material having a first coefficient of thermal expansion and a first modulus of elasticity. The plurality of longitudinally extending elongated reinforcing members are of a second material having a second coefficient of thermal expansion less than the first coefficient of thermal expansion, and a second modulus of elasticity greater than the first modulus of elasticity, such that the composite structural component has an effective coefficient of thermal expansion in the longitudinal direction that is less than 25% of the first coefficient of thermal expansion.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and all benefit of U.S. ProvisionalPatent Application Ser. No. 62/247,828, filed on Oct. 29, 2015, forTHERMOPLASTIC COMPONENTS WITH REDUCED COEFFICIENT OF THERMAL EXPANSION,the entire disclosure of which is fully incorporated herein byreference.

BACKGROUND

In the aviation and aerospace industries, devices and their packagestructures consist of a variety of metallic, ceramic, plastic, orcomposite components with vastly different coefficients of thermalexpansion (CTE). Mechanical failures in such devices can be caused bythermal expansion mismatch among the materials during fabrication orservice.

Lightweight thermoplastic materials (e.g., thermoplastic foams) arecommonly applied in the aerospace and aviation industries to themanufacture of ducts, seals, and other components. These materials havea characteristically higher CTE than the surrounding structural elementsto which the thermoplastic components are connected. For example,thermoplastic foams typically have a CTE of about 75-150×10⁻⁶/° F. (or75-150 μ/° F.), and other thermoplastics (e.g., nylon, ABS, PVC)typically have a CTE of about 30-60 μ/° F., as compared to other commonsystem materials, such as aluminum (about 13 μ/° F.) and steel (about 7μ/° F.). A problem that may arise is thermally induced stresstransferred to adjacent components with mismatched CTE. While mismatchedexpansion or contraction of thermoplastic parts may be mitigated bybonding these parts along their entire length to an adjacent structurewith lower CTE, such attachment may cause the thermoplastic part tobecome anisotropic or demonstrate a weak axis of bending, which couldcause the thermoplastic part to warp or otherwise deform through normalhandling and use.

SUMMARY

The present application contemplates the construction and use ofstructural components (e.g., ducts) formed from a material having a highCTE and reinforced with reinforcing members formed from a materialhaving a lower CTE, to produce a composite structural component having adesired effective CTE (e.g., a CTE that approximates or approaches theCTE of one or more components with which the composite structuralcomponent is connected). Accordingly, in one exemplary embodiment, acomposite structural component includes a longitudinally extendingelongated base element and a plurality of longitudinally extendingelongated reinforcing members each secured to the base element along alength of the reinforcing member at spaced apart locations on thethermoplastic element. The base element is of a first material having afirst coefficient of thermal expansion and a first modulus ofelasticity. The plurality of longitudinally extending elongatedreinforcing members are of a second material having a second coefficientof thermal expansion less than the first coefficient of thermalexpansion, and a second modulus of elasticity greater than the firstmodulus of elasticity, such that the composite structural component hasan effective coefficient of thermal expansion in the longitudinaldirection that is significantly less than the first coefficient ofthermal expansion (e.g., less than 50% of the first coefficient ofthermal expansion, less than 25% of the first coefficient of thermalexpansion, or less than 15% of the first coefficient of thermalexpansion).

In another exemplary embodiment, a method of forming a composite duct iscontemplated. In the exemplary method, a sheet of thermoplastic materialis provided, having first and second opposed surfaces extending to firstand second edges, with the thermoplastic material having a firstcoefficient of thermal expansion and a first modulus of elasticity. Thefirst and second edges are joined along a seam to form a duct, with thefirst sheet surface facing inward and the second sheet surface facingoutward. A plurality of elongated reinforcing members are secured to thesheet of thermoplastic material at spaced apart locations, with thesecured plurality of elongated reinforcing members extending in thelongitudinal direction. The plurality of elongated reinforcing membersare formed from a reinforcing material having a second coefficient ofthermal expansion less than the first coefficient of thermal expansionand a second modulus of elasticity greater than the first coefficient ofthermal expansion, such that the composite duct has an effectivecoefficient of thermal expansion in the longitudinal direction that issignificantly less than the first coefficient of thermal expansion(e.g., less than 50% of the first coefficient of thermal expansion, lessthan 25% of the first coefficient of thermal expansion, or less than 15%of the first coefficient of thermal expansion).

In another exemplary embodiment, a structural assembly includes asupport member of a first material having a first coefficient of thermalexpansion and a first modulus of elasticity, and a composite structuralcomponent connected to the support member. The composite structuralcomponent includes a base element and a plurality of longitudinallyextending reinforcing members, each secured to the base element along alength of the reinforcing member at spaced apart locations on the baseelement. The base element is of a second material having a secondcoefficient of thermal expansion and a second modulus of elasticity,with the second coefficient of thermal expansion being greater than thefirst coefficient of thermal expansion. The base element extendslongitudinally along the length of the composite structural component.The plurality of longitudinally extending reinforcing members are of athird material having a third coefficient of thermal expansion less thanthe second coefficient of thermal expansion, and a third modulus ofelasticity greater than the second modulus of elasticity, such that thecomposite structural component has an effective coefficient of thermalexpansion in the longitudinal direction that approaches the firstcoefficient of thermal expansion (e.g., within 30 μ/° F., within 10 μ/°F., or within 5 μ/° F.).

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, which are incorporated in and constitute apart of this specification, embodiments of the invention areillustrated, which, together with a general description of the inventiongiven above, and the detailed description given below, serve toexemplify the principles of this invention, wherein:

FIG. 1 is a perspective schematic view of an assembly including acomposite component connected along its length with a structuralelement;

FIG. 2 is a cross-sectional schematic end view of a composite duct, inaccordance with an exemplary embodiment;

FIG. 2A is a perspective view of a reinforcing member for a compositecomponent, in accordance with an exemplary embodiment;

FIG. 2B is a perspective view of another reinforcing member for acomposite component, in accordance with an exemplary embodiment;

FIG. 3 is a cross-sectional end view of another composite duct, inaccordance with an exemplary embodiment;

FIG. 4 is a cross-sectional end view of another composite duct, inaccordance with an exemplary embodiment;

FIG. 5 is a cross-sectional end view of another composite duct, inaccordance with an exemplary embodiment;

FIG. 6 is a cross-sectional end view of another composite duct, inaccordance with an exemplary embodiment;

FIG. 7 is a cross-sectional end view of another composite duct, inaccordance with an exemplary embodiment;

FIG. 8 is a cross-sectional end view of another composite duct, inaccordance with an exemplary embodiment;

FIG. 9 is a cross-sectional end view of another composite duct, inaccordance with an exemplary embodiment;

FIG. 10 is a perspective view of another composite duct, in accordancewith an exemplary embodiment; and

FIG. 11 is a perspective view of another composite duct, in accordancewith an exemplary embodiment.

DETAILED DESCRIPTION

The present application is directed towards systems and arrangements inwhich structural components formed from materials having a highcoefficient of thermal expansion (CTE), such as thermoplastic foam(e.g., PVDF) are subjected to large fluctuations in temperature, forexample, temperatures ranging from −65° F. to 300° F., or from −65° F.to 160° F. The application contemplates a variety of arrangements inwhich low CTE reinforcing members are secured to a high CTE base elementof a system component, either to minimize the effective CTE of thecomposite (i.e., base member with reinforcements) component, or toselectively modify the effective CTE to approximate (e.g., within 30 μ/°F., within 10 μ/° F., or within 5 μ/° F.) the CTE of a structuralcomponent with which the composite component is connected over at leasta portion of its length. Exemplary applications include, for example,aviation and aerospace applications in which lightweight thermoplasticfoam ducts are reinforced with low CTE reinforcing strips to provide alightweight composite duct having a lower effective CTE, as compared toan unreinforced thermoplastic foam duct, and in some applications, aneffective CTE that more closely matches the CTE of a component withwhich the composite duct is connected. The inventive features describedherein may additionally or alternatively be used in a wide variety ofother applications, including, for example, other types of high CTEmaterials (e.g., other thermoplastics, including, for example, nylon,polypropylene, and polyehtylene), other types of components (e.g.,seals, brackets, panels), and other types of temperature varyingapplications.

According to an aspect of the present application, a structuralcomponent constructed from a high CTE material may be constructed,adapted or otherwise produced with reinforcing members of a low CTEmaterial to produce a composite component having a reduced effectiveCTE, to reduce thermal expansion (or contraction) during thermal cyclingof the component. Where the structural component is an elongated,substantially linear component (e.g., a straight duct), the reinforcingmembers may be secured to the component to extend longitudinally alongthe length of the component, with the reinforcing members arrangedacross and/or around the component.

Applicants have determined that the effective linear coefficient ofthermal expansion of a uniform linear reinforced component (CTE_(eff))may be approximated as:

${C\; T\; E_{eff}} = \frac{{\left( {C\; T\; E_{d}} \right)\left( E_{d} \right)\left( A_{d} \right)} + {\left( {C\; T\; E_{r}} \right)\left( E_{r} \right)\left( A_{r} \right)}}{{\left( E_{d} \right)\left( A_{d} \right)} + {\left( E_{r} \right)\left( A_{r} \right)}}$

in which CTE_(d) is the coefficient of thermal expansion of the high CTEbase element duct material, E_(d) is the modulus of elasticity of theduct material, A_(d) is the cross-sectional area of the duct, CTE_(r) isthe coefficient of thermal expansion of the reinforcing member material,E_(r) is the modulus of elasticity of the reinforcing member material,and A_(r) is the total (combined) cross-sectional area of thereinforcing members. As can be appreciated from this formula, thecontribution of the reinforcing members to the effective CTE may beincreased by increasing the total cross-sectional area of thereinforcing members (generally not preferred due to size, weight, andmaterial cost considerations) or by increasing the modulus of elasticityof the reinforcing members.

By utilizing a reinforcing member material having a relatively low CTE(e.g., less than 60μ/° F., less than 40μ/° F., less than 20μ/° F., orless than 10μ/° F.) and a relatively high modulus of elasticity (e.g.,greater than 300 KSI, greater than 500 KSI, greater than 5000 KSI, orgreater than 10,000 KSI), the effective CTE of the composite componentis significantly reduced by the reinforcing members (e.g., such thatCTE_(eff) is less than 50% of CTE_(d), less than 25% of CTE_(d), or lessthan 15% of CTE_(d), even if the reinforcing members are relativelysmall in cross-sectional area (as compared to the duct). Where the ductis constructed of a material having a very small modulus of elasticity(e.g., less than 50 KSI, less than 10 KSI, or less than 1 KSI), such as,for example, thermoplastic foam (having a modulus of elasticity ofapproximately 0.5 KSI) and the reinforcing members are constructed of amaterial having a very large modulus of elasticity, such as, forexample, carbon fiber/thermoplastic composites (having a modulus ofelasticity of in the range of 5000-10,000 KSI) or aluminum (having amodulus of elasticity of approximately 10,000 KSI), the effective CTE ofthe composite duct approaches the CTE of the reinforcing members (e.g.,within 10%, 5%, or 1% of CTE_(r)), even where the total cross-sectionalarea of the reinforcing members is very small (e.g., less than 5%, 3%,or 1% of the cross-sectional area of the duct). This allows for the useof minimal amounts of reinforcing material (as compared to a sheath orwrap around the entire high CTE material component), minimizing materialcosts and component weight. A variety of materials having a relativelylow CTE (at least compared to thermoplastic foam) and a relatively highmodulus of elasticity may be used, including, for example,thermoplastics (e.g., Ultem®), composites of fiber (e.g., carbon fiber,glass fiber, aramid fiber) and thermoplastic (e.g., PEKK), fiberreinforced thermosets (e.g., fiberglass reinforced polyester), ceramics,and metals (e.g., aluminum, steel). As one example, a fiber (e.g.,carbon fiber, glass fiber, aramid fiber) may be encapsulated inthermoplastic, thermosetting plastic, or epoxy to form the reinforcingcomposite.

FIG. 1 schematically illustrates a structural assembly 5 of a reinforcedthermoplastic (or other high CTE material) composite component 10,reinforced with one or more reinforcing members 31, 32, 33 along alength of the component, and connected with a lower CTE structuralmember 50 (e.g., a wall, frame, or other structural component) at one ormore locations 51, 52, 53 (either discrete or continuous) along thelength of the composite component. These connections may comprise, forexample, fasteners, brackets, clamps, fluid couplings, or other suchcomponents or arrangements. A conventional structural support component(e.g., an airframe) is typically provided in a material having arelatively low coefficient of thermal expansion (e.g., less than 15 μ/°F.), such as a fiber/thermoplastic composite (e.g., carbon, aramid orglass fiber composites) or a metal (e.g., aluminum, steel, or titanium).To minimize any thermal expansion mismatch between the compositecomponent 10 and the connected structural member 50, one or more of thenumber, size, and material of the reinforcing members 31, 32, 33 securedto the high CTE material (e.g., thermoplastic foam) base element 20 ofthe composite component 10 may be selected such that the effective CTEof the composite component 10 approximates or approaches the CTE of theconnected structural component 50 (e.g., within 30 μ/° F., within 10 μ/°F., or within 5 μ/° F.), at least along the connected portions of thetwo components 10, 50, and at least along the elongated, longitudinallyextending portions of the composite component 10. As one example, bylimiting the differential CTE of the composite component 10 and thestructural component 50 to 30 μ/° F., the thermal expansion mismatch ofa 4 foot long composite component (relative to the connected structuralcomponent) is limited to approximately 0.32 inches when exposed to a225° F. change in temperature.

As shown, in some applications, where a portion 10 a of the compositecomponent 10 is not attached to an external structure, this portion ofthe component may optionally be provided without reinforcement where theunmodified expansion or contraction of this portion of the componentwill not produce a significant thermal expansion mismatch or otherundesirable stresses. Additionally or alternatively, in applicationswhere the component 10 includes non-longitudinally extending portions 10b (e.g., bends, flanges, etc.), these portions of the compositecomponent may optionally be provided without reinforcement where thecontribution to thermal expansion in the longitudinal direction of theseportions is not significant. Further, while the reinforcing members areshown as extending over the entire length of the linear, longitudinallyextending portions of the composite component, in other embodiments, thereinforcement member may extend along only a portion of the linear,longitudinally extending component portions (e.g., as is sufficient toachieve a desired effective CTE). Further, the reinforcing members mayform discontinuous, longitudinally extending segments along the linear,longitudinally extending component portions (e.g., as is sufficient toachieve a desired effective CTE).

While reinforcing members may be secured to a high CTE component in anysuitable arrangement, in one embodiment, a plurality of longitudinallyextending reinforcing members are substantially evenly spaced around acentroid of the high CTE component, to avoid non-uniform thermalexpansion/contraction, the formation of a weak bending axis, or otheranisotropic behavior of the component. In an exemplary embodiment, asshown in FIG. 1, at least three low CTE material reinforcing members 31,32, 33 are secured to the high CTE material base element 20 at locationsevenly spaced about the longitudinal center line or axis X of the baseelement 20.

The base element may form a wide variety of shapes in cross-section,including circular, square, rectangular, or irregular shaped (e.g.,L-shaped, T-shaped), and may be solid or hollow. In an exemplaryembodiment, the base element is a tubular cylindrical duct. While thebase elements shown herein are described as having a substantiallyuniform cross-sectional shape along their entire length, in otherembodiments, a base element may be non-uniform in shape along its length(for example, having enlarged, necked down, flanged, or otherwisediscontinuously shaped portions along its length).

A thermoplastic cylindrical duct may be formed using a variety ofprocesses, including, for example, machining, extruding, molding, andwelding. In an exemplary embodiment, a sheet of thermoplastic materialis molded into a tubular element in which first and second edges of thesheet are joined along a seam, for example, by thermal welding oradhesive bonding the first and second edges together. The edges of thesheet may be beveled, crenulated, or otherwise shaped to facilitateformation of a seam having a wall thickness substantially uniform withthe wall thickness of the sheet. Exemplary methods for forming acylindrical duct from a sheet of thermoplastic foam material aredescribed, for example, in U.S. Patent Application Pub. No.2008/0308674, the entire disclosure of which is incorporated herein byreference.

Reinforcing members may be attached to, embedded in, or otherwisesecured to a thermoplastic base duct member using a variety ofarrangements. Exemplary embodiments of reinforcing members secured tocylindrical duct base elements are disclosed in FIGS. 2-11 and describedbelow. Many of these embodiments may additionally or alternatively beused to secure reinforcing members to different shaped base elements,including, for example, different shaped (e.g., square, rectangular,oval) hollow base elements or ducts, different shaped solid baseelements, and irregularly shaped or non-uniform base elements.

In one embodiment, as shown in FIG. 2, a composite duct 100 may includea cylindrical tubular base element 120 (formed, for example, from arolled sheet of thermoplastic material joined along a seam portion 129)having series of longitudinal slits 121, 122, 123 formed in alongitudinally extending surface of the base element 120 and sized toretain the reinforcing members 131, 132, 133 therein. While thereinforcing members may be provided in a variety of cross-sectionalshapes (e.g., rectangular, circular, wedge-shaped, or more irregularcross-sections), in one embodiment, as shown, the reinforcing members131, 132, 133 are substantially flat strips sized to fit in therelatively narrow slits 121, 122, 123 and to provide sufficient surfacecontact with the slits for adhesion (both the retain the strip and tostrengthen the slit portions of the duct). The slits may be provided ata suitable depth to receive the reinforcing members and be resealed(e.g., using adhesive, thermal bonding, or some other suitable process)without compromising the structural integrity of the duct 100, and maybe angled with respect to the wall thickness to provide a suitable depthwithout cutting through the entire wall thickness of the duct. The slitsmay be spaced apart from the seam portion 129 of the tubular baseelement 120, for example, to avoid disrupting or otherwise compromisingthe seam seal.

The reinforcing members may be retained in the slits and secured to thebase element material along the length of the reinforcing member, forexample, using an adhesive, thermal bond, friction and/or interferencefit, or deformation of the heated base element material into aperturesor other such features of the reinforcing member. In one exemplaryembodiment, as shown in FIG. 2A, a reinforcing member 131 a may includeprotuberances 135 a or other discontinuities that provide aninterference or friction fit with the base element material,particularly if the base element material is permitted to flow or deformaround these protuberances 135 a. In another exemplary embodiment, asshown in FIG. 2B, a reinforcing member 131 b may include recesses 135 bor other discontinuities that provide an interference or friction fitwith the base element material, particularly if the base elementmaterial is permitted to flow or deform into these recesses 135 b.

While any number of reinforcing members may be provided, in oneembodiment, at least three reinforcing members are utilized (e.g.,between three and eight reinforcing members). The number of reinforcingmembers secured to the base element may depend, for example, on the sizeof the base element (with more reinforcing members used with a largerbase element), the cross-sectional shape of the base element (with morereinforcing members used to limit thermal expansion/contraction ondiscrete irregular portions of the base element), the size of thereinforcing members (i.e., fewer larger reinforcing members or moresmaller reinforcing members), and the amount that the CTE needs to bereduced (with more reinforcing members used to provide a greaterreduction in the effective CTE). In some applications, the use of agreater number of reinforcing members around the periphery of thecomposite component may provide for a more uniform adjusted effectiveCTE over the entire cross-section of the component. For example, byusing eight reinforcing members positioned at 45° increments around acylindrical component instead of three reinforcing members positioned at120° increments, the portions of the base element between thereinforcing members may be less affected by deviations in local thermalexpansion. Also, while the exemplary embodiments described hereininclude reinforcing members of uniform length, cross-sectional shape,and material, in other embodiments, the reinforcing members in acomposite component may have differing lengths, cross-sectional shapes,and materials, for example, to balance the thermal expansion ofdifferent portions of the composite component cross-section.

The longitudinal slits 121, 122, 123 may be formed in the base element120 in a variety of ways, including machining, mechanical cutting, andthermal cutting (e.g., by pressing a heated reinforcing member againstthe thermoplastic foam duct to form a slit closely receiving the heatedreinforcing member. Where the base element is formed from a heat rolledsheet of thermoplastic material, the slits may be formed in the sheetprior to rolling, or in the formed base element duct. Likewise, thereinforcing members 131, 132, 133 may be installed in the slits in thesheet prior to rolling or after the sheet has been rolled to form thecylindrical duct.

In the embodiment of FIG. 2, the longitudinal slits 121, 122, 123 areformed in an interior surface of the tubular base element 120. Inanother embodiment, as shown in FIG. 3, a composite duct 200 may includea cylindrical tube base element 220 (formed, for example, from a rolledsheet of thermoplastic material joined along a seam portion 229) havinga series of longitudinal slits 221, 222, 223 formed in an exteriorsurface of the tubular base element 220 and sized to retain thereinforcing members 231, 232, 233 therein, using any of the variety ofarrangements and processes described above. In still other embodiments(not shown), a base element may be provided with slits in both the outerand inner surfaces of the base element, for retention of outerperipheral and inner peripheral reinforcing members. Such an arrangementmay be desirable for hollow composite components having especially largewall thicknesses, to minimize any thermal expansion mismatch between theouter and inner surfaces of the duct.

In another embodiment, reinforcing members may be fully embedded in orsurrounded by the base element material, for example, by inserting thereinforcing members in longitudinally extending bores machined, drilled,or otherwise formed in the base element (either in the finished baseelement or in a sheet of material to be rolled or otherwise formed intothe base element duct or other such shape). In the embodiment of FIG. 4,a composite duct 300 includes a cylindrical tubular base element 320(formed, for example, from a rolled sheet of thermoplastic materialjoined along a seam portion 329) having a series of longitudinal bores321, 322, 323 sized to retain reinforcing members 331, 332, 333. Thereinforcing members may be secured in the bores by adhesive bonding,thermal bonding, interference fit with the deformed base elementmaterial, or any other suitable arrangement. While shown at a uniformdistance from the center line of the duct, in other embodiments, thereinforcing members may be positioned at varying distances from thecenter line, for example, to minimize any thermal expansion mismatchacross the cross-section of the composite component.

In another embodiment, reinforcing members may be bonded between pliesor sheets of a multiple layer or laminated base element duct. In onesuch embodiment, one or more sheets of the base element material (e.g.,separate sheets, or a spiral wrapped sheet) may form separatecylindrical layers of the base element, with the reinforcing membersbeing bonded or sandwiched between the cylindrical layers. In theembodiment of FIG. 5, a composite duct 400 includes a base element 420including an inner cylindrical layer 420 a (formed, for example, from arolled sheet of thermoplastic material joined along a seam portion 429a) and an outer cylindrical layer 420 b (formed, for example, from arolled sheet of thermoplastic material joined along a seam portion 429b), and reinforcing members 431, 432, 433 equally spaced around thecircumference of the base element 420 and bonded between the inner andouter layers 420 a, 420 b. As shown, the reinforcing members 431, 432,433 may be formed as relatively flat strips of material to facilitatebonding between the laminated base element layers. The reinforcingstrips may be secured in place, prior to duct lamination, by adhesive,thermal bonding, or any other suitable arrangement. While the inner andouter cylindrical layers 420 a, 420 b may be formed from the samematerial (e.g., the same thermoplastic foam material), in anotherembodiment, the inner and outer cylindrical layers may be formed fromdifferent materials, which may (but need not) have differentcoefficients of thermal expansion. In one such example, the reinforcingmembers bonded between the base element layers may serve to mitigate thethermal expansion mismatch of the two layers.

In another such embodiment, one or more longitudinally extending stripsof a base element material may be bonded against a cylindrical layer ofthe base element to cover and effectively embed the reinforcing members.In the embodiment of FIG. 6, a composite duct 500 includes a baseelement 520 having an inner cylindrical layer 520 a (formed, forexample, from a rolled sheet of thermoplastic material joined along aseam portion 529 a) and a discontinuous outer layer 520 b including aplurality of longitudinally extending strips 521 b, 522 b, 523 b bondedagainst the outer surface of the inner cylindrical layer 520 a to covercorresponding reinforcing members 531, 532, 533 equally spaced aroundthe circumference of the base element 520 and captured between the innerand outer layers 520 a, 520 b. As shown, the strips 521 b, 522 b, 523 bmay be retained in complementary shaped recesses 521 a, 522 a, 523 a inthe outer surface of the inner cylindrical layer 520 a to provide a baseelement duct having a substantially uniform wall thickness. In otherembodiments (not shown), strips of base element material may be bondedto a non-recessed exterior surface of the inner cylindrical layer. Asshown, the reinforcing members 531, 532, 533 may be formed as relativelyflat strips of material to facilitate bonding between the laminated baseelement layers. The reinforcing strips may be secured in place, prior toduct lamination, by adhesive, thermal bonding, or any other suitablearrangement. While the inner and outer layers 520 a, 520 b may be formedfrom the same material (e.g., the same thermoplastic foam material), inanother embodiment, the inner and outer layers may be formed fromdifferent materials, which may (but need not) have differentcoefficients of thermal expansion. In one such example, the reinforcingmembers bonded between the base element layers may serve to mitigate thethermal expansion mismatch of the two layers.

In another embodiment, as shown in FIG. 7, a composite duct 600 includesa base element 620 having an outer cylindrical layer 620 b (formed, forexample, from a rolled sheet of thermoplastic material joined along aseam portion 629 b) and a discontinuous inner layer 620 a including aplurality of longitudinally extending strips 621 a, 622 a, 623 a bondedagainst the inner surface of the outer cylindrical layer 620 b to covercorresponding reinforcing members 631, 632, 633 equally spaced aroundthe circumference of the base element 620 and captured between the innerand outer layers 620 a, 620 b. As shown, the strips 621 a, 622 a, 623 amay be retained in complementary shaped recesses 621 b, 622 b, 623 b inthe inner surface of the outer cylindrical layer 620 b to provide a baseelement duct having a substantially uniform wall thickness. In otherembodiments (not shown), strips of base element material may be bondedto a non-recessed interior surface of the outer cylindrical layer. Asshown, the reinforcing members 631, 632, 633 may be formed as relativelyflat strips of material to facilitate bonding between the laminated baseelement layers. The reinforcing strips may be secured in place, prior toduct lamination, by adhesive, thermal bonding, or any other suitablearrangement. While the inner and outer layers 620 a, 620 b may be formedfrom the same material (e.g., the same thermoplastic foam material), inanother embodiment, the inner and outer layers may be formed fromdifferent materials, which may (but need not) have differentcoefficients of thermal expansion. In one such example, the reinforcingmembers bonded between the base element layers may serve to mitigate thethermal expansion mismatch of the two layers.

In another embodiment, reinforcing members may be directly bonded (e.g.,by adhesive or thermal bonding) to a surface of the base element in alongitudinal direction to extend along a length of the base element. Insuch an embodiment, the reinforcing members may be formed as relativelyflat strips of material to minimize changes to the cross-sectional shapeof the composite duct. Additionally or alternatively, the reinforcingmembers may be at least partially pressed into the based elementmaterial (e.g., when the material is in a softened, heated condition),to facilitate adhesion of the reinforcing members and/or to minimizechanges to the cross-sectional shape of the composite duct. Thereinforcing strips may be secured in place by adhesive bonding, thermalbonding, interference fit with the deformed base element material,adhesive tape (e.g., metallized tape) applied over the reinforcingmember and adjacent base element surfaces, or any other suitablearrangement.

In the embodiment of FIG. 8, a composite duct 700 includes a tubularduct base element 720 (formed, for example, from a rolled sheet ofthermoplastic material joined along a seam portion 729) and a pluralityof longitudinally extending reinforcing members 731, 732, 733 directlybonded to an outer surface of the base element 720 and evenly spacedaround the periphery of the base element. The reinforcing strips may besecured in place by adhesive bonding, thermal bonding, interference fitwith the deformed base element material, adhesive tape 740 (e.g.,metallized tape) applied over the reinforcing member and adjacent baseelement surfaces, or any other suitable arrangement. In the embodimentof FIG. 9, a composite duct 800 includes a tubular duct base element 820(formed, for example, from a rolled sheet of thermoplastic materialjoined along a seam portion 829) and a plurality of longitudinallyextending reinforcing members 831, 832, 833 directly bonded to an innersurface of the base element 820 and evenly spaced around the peripheryof the base element. The reinforcing strips may be secured in place byadhesive bonding, thermal bonding, interference fit with the deformedbase element material, adhesive tape 840 (e.g., metallized tape) appliedover the reinforcing member and adjacent base element surfaces, or anyother suitable arrangement. In still other embodiments (not shown), abase element may be provided with reinforcing strips bonded to both theouter and inner surfaces of the base element. Such an arrangement may bedesirable for hollow composite components having especially large wallthicknesses, to minimize any thermal expansion mismatch between theouter and inner surfaces of the duct.

In the exemplary embodiments of FIGS. 1-9, the reinforcing members arelimited to longitudinally extending members spaced apart from eachother, and not interconnected with each other. In this arrangement, theamount and weight of reinforcing material may be minimized whileeffectively reducing or otherwise controlling thermal expansion in thelongitudinal direction, the primary dimension along which the elongatedcomponent would have experienced thermal expansion. In otherembodiments, a high CTE material component that extends substantially intwo directions (e.g., both longitudinal and lateral directions, as isthe case with a plate shaped member) may include reinforcing membersthat extend in these two directions, to reduce the effective CTE in bothdirections.

In still other embodiments, interconnected reinforcing members may beutilized to facilitate attachment of a large number of reinforcingmembers to the base element (e.g., to the outer surface, inner surface,or embedded between layers of a base element duct). In the exemplaryembodiment of FIG. 10, a composite duct 900 includes a cylindricaltubular base element 920 (formed, for example, from a rolled sheet ofthermoplastic material joined along a seam portion 929) having areinforcing mesh 930 secured to an outer surface of the base element920, for example, by adhesive bonding, thermal bonding, interference fitwith the deformed base element material, a second base element layer(which may be similar to the embodiment of FIG. 5), or any othersuitable arrangement. The exemplary mesh 920 includes longitudinallyextending parallel reinforcing strands 931 and laterally orcircumferentially extending parallel connecting strands 932. In oneembodiment, the entire mesh is provided in a low CTE, high modulus ofelasticity reinforcing material for improvement of the effective CTE. Inanother embodiment, the reinforcing strands 931 are provided in a lowCTE, high modulus of elasticity reinforcing material, and the connectingstrands 932 are provided in another, non-critical material (which mayhave a high CTE or a low modulus of elasticity), as thecircumferentially extending connecting strands do not significantlycontribute to the effective longitudinal CTE. The large number ofsmaller reinforcing strands 931 positioned around the circumference ofthe composite duct 900 may provide for a more uniform distribution ofthe reduced effective CTE around the entire circumference of the duct900. The smaller size of the strands may also facilitate post-productionmachining and cutting operations on the duct (as compared to having tocut through larger, rigid reinforcing members).

In another embodiment, as shown in FIG. 11, a reinforcing mesh 1030 maybe arranged to have an array of crossing reinforcing strands 1031, 1032oriented such that all of the mesh strands 1031, 1032 extend at leastpartially in the longitudinal direction, such that all of the crossingreinforcing strands contribute to a reduction in the effective CTE ofthe composite duct 1000.

In other embodiments (not shown), a reinforcing mesh, such as, forexample, one of the reinforcing meshes 930, 1030 of FIGS. 10 and 11 maybe applied to an inner surface of a base element duct, or embeddedbetween layers of a base element duct.

While various inventive aspects, concepts and features of the inventionsmay be described and illustrated herein as embodied in combination inthe exemplary embodiments, these various aspects, concepts and featuresmay be used in many alternative embodiments, either individually or invarious combinations and sub-combinations thereof. Unless expresslyexcluded herein all such combinations and sub-combinations are intendedto be within the scope of the present inventions. Still further, whilevarious alternative embodiments as to the various aspects, concepts andfeatures of the inventions—such as alternative materials, structures,configurations, methods, devices and components, alternatives as toform, fit and function, and so on—may be described herein, suchdescriptions are not intended to be a complete or exhaustive list ofavailable alternative embodiments, whether presently known or laterdeveloped. Those skilled in the art may readily adopt one or more of theinventive aspects, concepts or features into additional embodiments anduses within the scope of the present inventions even if such embodimentsare not expressly disclosed herein. Additionally, even though somefeatures, concepts or aspects of the inventions may be described hereinas being a preferred arrangement or method, such description is notintended to suggest that such feature is required or necessary unlessexpressly so stated. Still further, exemplary or representative valuesand ranges may be included to assist in understanding the presentdisclosure; however, such values and ranges are not to be construed in alimiting sense and are intended to be critical values or ranges only ifso expressly stated. Moreover, while various aspects, features andconcepts may be expressly identified herein as being inventive orforming part of an invention, such identification is not intended to beexclusive, but rather there may be inventive aspects, concepts andfeatures that are fully described herein without being expresslyidentified as such or as part of a specific invention, the inventionsinstead being set forth in the appended claims. Descriptions ofexemplary methods or processes are not limited to inclusion of all stepsas being required in all cases, nor is the order that the steps arepresented to be construed as required or necessary unless expressly sostated.

What is claimed is:
 1. A composite structural component comprising: alongitudinally extending elongated base element of a first materialhaving a first coefficient of thermal expansion and a first modulus ofelasticity; and a plurality of longitudinally extending elongatedreinforcing members of a second material, each secured to the baseelement along a length of the reinforcing member at spaced apartlocations on the base element, the second material having a secondcoefficient of thermal expansion less than the first coefficient ofthermal expansion, and a second modulus of elasticity greater than thefirst modulus of elasticity, such that the composite structuralcomponent has an effective coefficient of thermal expansion in thelongitudinal direction that is less than 25% of the first coefficientsof thermal expansion.
 2. The composite structural component of claim 1,wherein the plurality of reinforcing members together have a totalcross-sectional area that is less than 1% of a total cross-sectionalarea of the base element.
 3. The composite structural component of claim1, wherein the first material comprises a thermoplastic foam material.4. The composite structural component of claim 1, wherein the firstcoefficient of thermal expansion is at least about 75 μ/° F., and thesecond coefficient of thermal expansion is no greater than about 20 μ/°F.
 5. The composite structural component of claim 1, wherein the firstmodulus of elasticity is no greater than about 10 KSI, and the secondmodulus of elasticity is at least about 1000 KSI.
 6. The compositestructural component of claim 1, wherein the elongated base elementcomprises a tubular duct.
 7. The composite structural component of claim6, wherein the tubular duct includes at least one longitudinal seam, andwherein the at least one longitudinal seam is spaced apart from each ofthe plurality of reinforcing members.
 8. The composite structuralcomponent of claim 1, wherein at least one of the plurality ofreinforcing members is embedded in a peripheral wall of the elongatedbase element.
 9. The composite structural component of claim 8, whereineach of the plurality of reinforcing members is retained in acorresponding one of a plurality of longitudinally extending slits inthe peripheral wall.
 10. The composite structural component of claim 9,wherein the plurality of longitudinally extending slits are formed in anexternal surface of the peripheral wall.
 11. The composite structuralcomponent of claim 1, wherein the plurality of reinforcing memberscomprises at least three reinforcing members.
 12. The compositestructural component of claim 1, wherein each of the plurality ofreinforcing members is secured to the elongated base element by at leastone of a structural adhesive, thermal bonding, solvent weld bond,mechanical fasteners, and an interference fit with the elongated baseelement.
 13. A method of forming a composite duct, the methodcomprising: providing a sheet of thermoplastic material having first andsecond opposed surfaces extending to first and second edges, thethermoplastic material having a first coefficient of thermal expansionand a first modulus of elasticity; joining the first and second edgesalong a seam to form a duct, with the first sheet surface facing inwardand the second sheet surface facing outward; and securing a plurality ofelongated reinforcing members to the sheet of thermoplastic material atspaced apart locations, the secured plurality of elongated reinforcingmembers extending in the longitudinal direction; wherein the pluralityof elongated reinforcing members are formed from a reinforcing materialhaving a second coefficient of thermal expansion less than the firstcoefficient of thermal expansion and a second modulus of elasticitygreater than the first coefficient of thermal expansion, such that thecomposite duct has an effective coefficient of thermal expansion in thelongitudinal direction that is less than 25% of the first coefficient ofthermal expansion.
 14. The method of claim 13, wherein securing theplurality of elongated reinforcing members to the sheet of thermoplasticmaterial comprises forming a plurality of longitudinally extending slitsin the sheet and receiving each of the plurality of elongatedreinforcing members in a corresponding one of the plurality oflongitudinally extending slits.
 15. The method of claim 13, whereinsecuring the plurality of elongated reinforcing members to the sheet ofthermoplastic material comprises use of at least one of at least one ofa structural adhesive, thermal bonding, a solvent weld bond, mechanicalfasteners, and an interference fit with the sheet of thermoplasticmaterial.
 16. A structural assembly comprising: a support member of afirst material having a first coefficient of thermal expansion and afirst modulus of elasticity; and a composite structural componentconnected to the support member along a length of the compositestructural component, comprising: an base element of a second materialhaving a second coefficient of thermal expansion and a second modulus ofelasticity, the second coefficient of thermal expansion being greaterthan the first coefficient of thermal expansion, the base elementextending longitudinally along the length of the composite structuralcomponent; and a plurality of longitudinally extending reinforcingmembers of a third material, each secured to the base element along alength of the reinforcing member at spaced apart locations on the baseelement, the third material having a third coefficient of thermalexpansion less than the second coefficient of thermal expansion, and athird modulus of elasticity greater than the second modulus ofelasticity, such that the composite structural component has aneffective coefficient of thermal expansion in the longitudinal directionthat is within 30 μ/° F. of the first coefficient of thermal expansion.17. The assembly of claim 16, wherein the first material comprises atleast one of metal and fiber/thermoplastic composite.
 18. The assemblyof claim 16, wherein the second material comprises a thermoplastic foammaterial.
 19. The assembly of claim 16, wherein the third materialcomprises one of a metal, a ceramic, a thermoplastic, a thermoplasticcomposite including at least one of carbon fiber, glass fiber, andaramid fiber, and a fiber reinforced thermoset including at least one ofcarbon fiber, glass fiber, and aramid fiber.
 20. The assembly of claim16, wherein the first coefficient of thermal expansion is no greaterthan 15 μ/° F.